// Copyright [2020] <unknown>
#include <bits/stdc++.h>
using namespace std;
// #define ONLINE_JUDGE
#ifndef ONLINE_JUDGE
#define dbg(x...) { cerr << "\033[32;1m" << #x << " -> "; err(x); }
void err() { cerr << "\033[39;0m" << endl; }
template<typename T, typename... A>
void err(T a, A... x) { cerr << a << ' '; err(x...); }
#else
#define dbg(...)
#endif

#define sz(x) ((int)x.size())

typedef long long LL;
const int N = 1e5+50;

int t, n, d;
int a[N];

int main(int argc, char const *argv[]) {
    // code
    scanf("%d", &t);
    for (int kk = 0; kk < t; ++kk) {
        scanf("%d%d", &n, &d);
        for (int i = 0; i < n; ++i)
            scanf("%d", &a[i]);
        for (int i = 1; i < n && d; ++i) {
            LL x = min(LL(d), 1LL * i * a[i]);
            d -= x;
            a[0] += x / i;
        }
        printf("%d\n", a[0]);
    }
        return 0;
}
